Similar to Example 4.5-2 in F&R, 3rd Ed.
One of our clients has asked our Bison Engineering and Evaluation Firm (BEEF, Inc.) to evaluate a
multi-unit chemical process that recovers solid potassium chromate salt from an aqueous solution. The
client has provide a description of the chemical process, as given in the next paragraph.
A feed stream of potassium chromate solution is sent to an evaporator where heat boils off some water
as steam and produces a concentrated solution containing 49.4 wt% K2CrO4. This concentrated stream
is fed into a crystallizer in which the solution is cooled causing potassium chromate crystals to form,
and then the solution with suspended crystals is filtered. The filter cake contains solid crystals with an
entrapped solution of 36.36 wt% dissolved K2CrO4. The crystals account for 95% of the total mass of
the filter cake. The solution that passes through the filter is recycled back to the beginning of the
multi-unit process. This recycle stream containing 36.36 wt% K2CrO4 is mixed with 4.500 x 103 kg/h
of a fresh aqueous solution to the multi-unit process that contains one-third potassium chromate by
mass. The resulting stream from the mixing is then fed into the evaporator.
Your project supervisor has asked you to complete the material balances on this multi-unit process.
You are to determine the flow rate of the steam leaving the evaporator, the rate of production of
crystalline K2CrO4, the feed rates that the evaporator and crystallizer must be designed to handle, and
the ratio (kg recycle per kg fresh feed). Also, what is the composition of the feed to the evaporator?
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Click here to view the Excel "EZ Setup"/
Solver file containing solutions of several
mathematical models and a mathematical
algorithm. This file also demonstrates the
financial benefit of recycling materials.
v90.10.04
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